The phase formation of cobalt germanides on Ge(100) and Ge(111) substrates was investigated using in situ X-ray diffraction, starting from room-temperature sputter-deposited Co films. The formation temperature of the CoGe2 phase was dependent on the substrate orientation. X-ray pole figures and electron backscatter diffraction measurements were used to identify the texture and microstructure of the CoGe2 and the preceding Co5 Ge7 films. A significant difference in preferential orientation was found in the Co5 Ge7 films, depending on the substrate orientation. This influences the formation temperature of the CoGe2 and results in the coexistence of Co5 Ge7 and CoGe 2 on Ge(111) in a large temperature window. © 2010 The Electrochemical Society.